Cache management based on types of I/O operations

ABSTRACT

A list of a first type of tracks in a cache is generated. A list of a second type of tracks in the cache is generated, wherein I/O operations are completed relatively faster to the first type of tracks than to the second type of tracks. A determination is made as to whether to demote a track from the list of the first type of tracks or from the list of the second type of tracks.

BACKGROUND

1. Field

Embodiments relate to cache management based on types of input/output(I/O) operations.

2. Background

In certain storage system environments, a storage controller (or astorage controller complex) may comprise a plurality of storage serversthat are coupled to each other. The storage controller allows hostcomputing systems to perform input/output (I/O) operations with storagedevices controlled by the storage controller, where the host computingsystems may be referred to as hosts.

The storage controller includes a cache that stores data so that futurerequests for that data from the host may be served faster. Data may bewritten to or read from the cache much faster in comparison to writingto or reading from the storage device. A cache hit occurs when requesteddata from the host can be found in the cache, while a cache miss occurswhen the requested data cannot be found in the cache. Cache hits areserved by reading data from the cache, which is faster than reading froma storage device coupled to the storage controller.

When a cache is low on space or segments, then the cache needs to evictdata items from the cache and this eviction of data items from the cacheis referred to as demotion. A cache replacement policy may be used todetermine which data items in the cache are to be demoted to make roomfor new data items. A least recently used (LRU) policy demotes the leastrecently used data items first.

SUMMARY OF THE PREFERRED EMBODIMENTS

Provided are a method, system, and computer program product in which alist of a first type of tracks in a cache is generated. A list of asecond type of tracks in the cache is generated, wherein I/O operationsare completed relatively faster to the first type of tracks than to thesecond type of tracks. A determination is made as to whether to demote atrack from the list of the first type of tracks or from the list of thesecond type of tracks. As a result of the determination, the tracks thatare demoted increase the rate of I/O operations.

In further embodiments, the first type of tracks are syncio tracks,wherein for performing an I/O operation to a syncio track, anapplication thread is held in a spin loop waiting for the I/O operationto complete. As a result, in certain embodiments it may be desirable notto demote syncio tracks, in order to increase the rate of I/Ooperations.

In yet further embodiments, the second type of tracks are non-synciotracks, wherein for performing the I/O operation to a non-syncio track,holding of the application thread in the spin loop is avoided, andwherein a track is added to the list of the first type of tracks or tothe list of the second type of tracks based on whether a last I/Ooperation performed on the track is a first type of I/O operationcomprising a syncio operation or a second type of I/O operationcomprising a non-syncio operation. As a result, the rate of I/Ooperations is increased by building two different types of lists.

In further embodiments, tracks in the list of the first type of tracksare ordered based on how recently each track in the list of the firsttype of tracks has been used, wherein tracks in the list of the secondtype of tracks are ordered based on how recently each track in the listof the second type of tracks has been used. As a result, the rate of I/Ooperations is increased by building two different types of leastrecently used lists of tracks.

In certain embodiments, in response to determining that a read hit ratiofor tracks in the list of the second type of tracks is less than apredetermined factor of a read hit ratio for tracks in the first type oftracks, a track is demoted from the list of the second type of tracks.As a result of demotion from the second type of tracks, the rate of I/Ooperations is increased.

In additional embodiments, the read hit ratio for tracks in the list ofthe first type of tracks and the read hit ratio for tracks in the listof the second type of tracks are computed based on read hits on apredetermined bottom portion of the list of the first type of tracks andthe second type of tracks. As a result, the demotion of tracks is basedon collecting statistics on a set of more recently used tracks.

In further embodiments, the predetermined factor is adjusted to increasea rate of input/output (I/O) operations. As a result, whenever it ispossible, tracks from a LRU list of non-syncio tracks are demoted ratherthan tracks from a LRU list of syncio tracks, unless the rate of I/Ooperations in the system decrease as a result of such demotions.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 illustrates a block diagram of a computing environment comprisinga storage controller coupled to one or more hosts and one or morestorage devices, where syncio based I/O operations occur from the hostto the storage controller, in accordance with certain embodiments;

FIG. 2 illustrates a block diagram that shows how least recently used(LRU) lists of tracks are maintained in the storage controller, inaccordance with certain embodiments;

FIG. 3 illustrates a first flowchart that shows demotion of tracks froma non-syncio LRU list or from a syncio LRU list, in accordance withcertain embodiments;

FIG. 4 illustrates a second flowchart that shows demotion of tracks froma non-syncio LRU list or from a syncio LRU list, in accordance withcertain embodiments;

FIG. 5 illustrates a flowchart that shows how a read hit ratio iscomputed, in accordance with certain embodiments;

FIG. 6 illustrates a block diagram that shows how a predetermined factorfor demotion of tracks is computed, in accordance with certainembodiments;

FIG. 7 illustrates a flowchart that shows demotion of tracks based ongenerating lists of two different types of tracks, in accordance withcertain embodiments;

FIG. 8 illustrates a block diagram of a cloud computing environment, inaccordance with certain embodiments;

FIG. 9 illustrates a block diagram of further details of the cloudcomputing environment of FIG. 8, in accordance with certain embodiments;and

FIG. 10 illustrates a block diagram of a computational system that showscertain elements that may be included in the storage controller or thehost, as described in FIGS. 1-9, in accordance with certain embodiments.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings which form a part hereof and which illustrate severalembodiments. It is understood that other embodiments may be utilized andstructural and operational changes may be made.

Syncio (also referred to as sync I/O) comprises an attachment hardwareand protocol for computational devices. Syncio is designed for very lowlatency random reads and small block sequential writes. Syncioconnections between computational devices may be over point to pointoptical Peripheral Component Interconnect Express (PCIe) interfaces.Syncio operations behave differently than traditional I/O in that insyncio a host computational device may hold an application thread in aspin loop while waiting for the I/O operation to complete. This avoidsthe need for processor cycles to perform the two context swaps oftraditional I/O, the need to perform operations for putting the I/Othread to sleep and then re-dispatching the I/O thread, and the need foran I/O interrupt.

The code path in a computational device needs to be extremely optimizedto meet the time requirements for syncio operation. Any condition whichdelays a syncio operation, such as a cache miss may generate a statusthat indicates that the syncio operation cannot be performed, and thesyncio operation may have to be retried. Since a syncio operation may besuccessfully performed only when there is a cache hit, certainembodiments are provided to increase cache hits for syncio operations.In such embodiments, by maintaining separate least recently used (LRU)lists for syncio tracks and non-syncio tracks and using demotionmechanisms based on the separate LRU lists, syncio operations arecompleted faster in comparison to embodiments in which only a single LRUlist is maintained. In certain embodiments, whenever it is possible,tracks from the LRU list of non-syncio tracks are demoted rather thantracks from the LRU list of syncio tracks, unless the rate of I/Ooperations in the system decrease as a result of such demotions.

Exemplary Embodiments

FIG. 1 illustrates a block diagram of a computing environment 100comprising a storage controller 102 coupled to one or more hosts 104,106, and one or more storage devices 108, 110, in accordance withcertain embodiments. The storage controller 102 allows the plurality ofhosts 104, 106 to perform input/output (I/O) operations with logicalstorage maintained by the storage controller 102. The physical storagecorresponding to the logical storage may be found in one or more of thestorage devices 108, 110 and/or a cache 112 (e.g., a memory) of thestorage controller 102.

The storage controller 102 and the hosts 104, 106 may comprise anysuitable computational device including those presently known in theart, such as, a personal computer, a workstation, a server, a mainframe,a hand held computer, a palm top computer, a telephony device, a networkappliance, a blade computer, a processing device, etc. The storagecontroller 102, the hosts 104, 106, and the storage devices 108, 110 maybe elements in any suitable network 114, such as, a storage areanetwork, a wide area network, the Internet, an intranet. In certainembodiments, the storage controller 102, the hosts 104, 106, and thestorage devices 108, 110 may be elements in a cloud computingenvironment that comprises the computing environment 100. The storagedevices 108, 110 may be comprised of storage disks, tape drives, solidstate storage, etc., and may be controlled by the storage controller102.

In certain embodiments, the hosts 104, 106 may be coupled to the storagecontroller 102 via a bus interface (e.g., a point to point optical PCIeinterface) 116, 118 and a network interface 120, 122. Syncio operationsfrom the hosts 104, 106 may be performed over the bus interfaces 116,118. Traditional I/O operations (i.e., non-syncio operations) from thehosts 104, 106 may be performed over the network interfaces 120, 122.The bus interfaces 116, 118 may comprise a faster access channel for I/Othan the network interfaces 120, 122. Additional bus interfacetechnology to extend the bus interface 116, 118 may be utilized,including PCIe extender cables or components, such as a distributed PCIeswitch, to allow PCIe over Ethernet, such as with the ExpEthertechnology.

The cache 112 may in certain embodiments may comprise a read/write cachepartitioned into one or more ranks, where each rank may include one ormore storage tracks. The cache 112 may be any suitable cache known inthe art or developed in the future. In some embodiments, the cache 112may be implemented with a volatile memory and/or non-volatile memory.The cache 112 may store both modified and unmodified data. The cache 112may store data in a plurality of tracks that include syncio tracks 124and non-syncio tracks 126. Syncio tracks 124 may be read from andwritten to via syncio operations 128 that are performed on the storagecontroller 102 from the hosts 104, 106, and non-syncio tracks 126 may beread from and written to via non-syncio I/O operations 130 that areperformed on the storage controller 102 from the hosts 104, 106. A cachemanagement application 132 generates a non-syncio least recently used(LRU) list 134 of unmodified syncio tracks in the cache 112 and syncioLRU list 136 of unmodified non-syncio tracks in the cache 112, where theunmodified syncio tracks and the unmodified non-syncio tracks arecandidates for demotion from the cache 112 to free up space in the cache112. In certain embodiments, the cache management application 132 may beimplemented in software, hardware, firmware or any combination thereof.

FIG. 2 illustrates a block diagram 200 that shows how LRU lists oftracks are maintained in the storage controller 102, in accordance withcertain embodiments.

The non-syncio LRU list 134 is a list of unmodified non-syncio tracks inthe cache 112 to which non-syncio operations may be performed, and thesyncio LRU list 136 is a list of unmodified syncio tracks in the cache112 to which syncio operations may be performed.

The entries in the non-syncio LRU list 134 are unmodified non-synciotracks in the cache 112 placed from top to bottom from the most recentlyused 202 to the least recently used 204. A number of predeterminedentries at the bottom portion 206 of the non-syncio LRU list 134 may beused for computing read hit ratio on the non-syncio LRU list 134. Byselecting only the bottom portion 206 (e.g., the 1000 least recentlyused non-syncio tracks in the non-syncio LRU list 134) for computing theread hit ratio on the non-syncio LRU list 134, the read hit ratio isdetermined for the potential tracks for demotion from the cache 112.

The entries in the syncio LRU list 136 are unmodified syncio tracks inthe cache 112 placed from top to bottom from the most recently used 208to the least recently used 210. A number of predetermined entries at thebottom portion 212 of the syncio LRU list 136 may be used for computingread hit ratio on the syncio LRU list 136. By selecting only the bottomportion 212 (e.g., the 1000 least recently used syncio tracks in thesyncio LRU list 136) for computing the read hit ratio on the syncio LRUlist 136, the read hit ratio is determined for the potential tracks fordemotion from the cache 112.

FIG. 3 illustrates a first flowchart 300 that shows demotion of tracksfrom a non-syncio LRU list or from a syncio LRU list, in accordance withcertain embodiments. The operations shown in FIG. 3 may be performed bythe cache management application 132 that executes in the storagecontroller 102.

Control starts at block 302 in which the cache management application132 generates and maintains the syncio LRU list 136. The cachemanagement application 132 determines (at block 304) the read hit ratiofor tracks in the syncio LRU list 136 and control returns to block 302.

In parallel to the operations shown in blocks 302, 304, the cachemanagement application 132 generates and maintains the non-syncio LRUlist 134 (at block 306). The cache management application 132 determines(at block 308) the read hit ratio for tracks in the non-syncio LRU list134 and control returns to block 306.

While the operations of blocks 302, 304, 306, 308 are being performed,the cache management application 132 continues or starts performing (atblock 310) operations for demoting tracks from the cache 112. The cachemanagement application 132 determines (at block 312) whether the readhit ratio for tracks in the non-syncio LRU list 134 is less than apredetermined factor (e.g., multiple) of read hit ratio for tracks inthe syncio LRU list 136. For example, if the read hit ratio for tracksin the non-syncio LRU list 134 is 0.2, the read hit ratio for tracks inthe syncio LRU list 136 is 0.1, and the predetermined factor is 3, thenthe read hit ratio for tracks in the syncio LRU list multiplied by thepredetermined factor is 0.3. The read hit ratio for tracks in thenon-syncio LRU list 134 is 0.2 which is less than 0.3. Therefore, inthis example, the read hit ratio for tracks in the non-syncio LRU list134 is less than a predetermined factor of read hit ratio for tracks inthe syncio LRU list 136.

If at block 312, it is determined that the read hit ratio for tracks inthe non-syncio LRU list 134 is less than the predetermined factor ofread hit ratio for tracks in the syncio LRU list 136 (“Yes branch 314),then the cache management application 132 demotes (at block 316) tracksfrom the non-syncio LRU list 134, and the performance of synciooperations may be enhanced over situations in which syncio tracks aredemoted. The tracks in the non-syncio LRU list 134 are being usedsufficiently less than the tracks in the syncio LRU list 136 and so itis desirable to demote from the non-syncio LRU list 134.

If at block 312 it is determined that the read hit ratio for tracks inthe non-syncio LRU list 134 is not less than the predetermined factor ofread hit ratio for tracks in the syncio LRU list 136 (“No” branch 318),then the cache management application 132 demotes (at block 320) tracksfrom the syncio LRU list 136. The tracks in the non-syncio LRU list 134are being used sufficiently more than the tracks in the syncio LRU list136 and so it is desirable to demote from the syncio LRU list 136. Theremay be relatively few read hits on tracks in the syncio LRU list 136 andso it is desirable to demote tracks from the syncio LRU list 136.

Therefore, FIG. 3 describes embodiments in which by maintainingdifferent LRU lists for syncio and non-syncio tracks, the synciooperations may be executed faster in comparison to embodiments in whichonly a single LRU list is maintained.

FIG. 4 illustrates a second flowchart that shows demotion of tracks froma non-syncio LRU list 134 or from a syncio LRU list 136 in accordancewith certain embodiments. The operations shown in FIG. 4 may beperformed by the cache management application 132 that executes in thestorage controller 102.

Control starts at block 402 in which the cache management application132 determines whether the syncio LRU list 136 is empty. If so (“Yes”branch 404) control proceeds to block 406 in which the cache managementapplication 132 demotes tracks from the non-syncio LRU list 134.Otherwise (“No” branch 408), control proceeds to block 410 in which thecache management application 132 determines whether the non-syncio LRUlist 134 is empty.

If at block 410, the cache management application 132 determines thatthe non-syncio LRU list 134 is empty (“Yes” branch 412), then the cachemanagement application 132 demotes tracks from the syncio LRU list 136.Otherwise (“No” branch 416) control proceeds to block 418 in which thecache management application 132 determines whether the oldest track ofthe non-syncio LRU list 134 is older than the oldest track of the syncioLRU list 136, where the oldest track of a list is the track that waslast used (i.e., read hit occurred on the track) at a time before thelast use of all other tracks in the list, and a first track that waslast used at a time before the last use of a second track is older thanthe second track.

If at block 418, the cache management application 132 determines thatthe oldest track of the non-syncio LRU list 134 is older than the oldesttrack of the syncio LRU list 136 (“Yes” branch 420) control proceeds toblock 422 in which the cache management application 132 demotes tracksfrom the non-syncio LRU list 134. Otherwise (“No” branch 424), the cachemanagement application 132 computes (at block 426) the read hit ratio onthe following: (a) bottom portion of syncio LRU list 212; and (b) bottomportion of non-syncio LRU list 206.

The read hit ratio on the bottom portion of syncio LRU list 212 isreferred to as SIO_BOTTOMHITS and the read hit ratio on the bottomportion of non-syncio LRU list 206 is referred to as NONSIO_BOTTOMHITS.

From block 426 control proceeds to block 428 in which the cachemanagement application 132 determines whether the NONSIO_BOTTOMHITS isless than the SIO_BOTTOMHITS multiplied by a predetermined factor. If so(“Yes” branch 430), the cache management application 132 demotes tracksfrom the non-syncio LRU list 134. Otherwise (“No” branch 434), the cachemanagement application 132 demotes (at block 436) tracks from the syncioLRU list 136.

Therefore, FIG. 4 illustrates certain embodiments in which at least thebottom portions 206, 212 of the non-syncio LRU list 134 and the syncioLRU list 136 are used for the comparison of read hits so that thecomparison is made of read hits on tracks that are relatively oldertracks in the non-syncio LRU list 134 and the syncio LRU list 136. Thedemotions of tracks are from these relatively older tracks so read hitratio is computed for these relatively older tracks.

FIG. 5 illustrates a flowchart 500 that shows how a read hit ratio iscomputed in accordance with certain embodiments. The operations shown inFIG. 5 may be performed by the cache management application 132 thatexecutes in the storage controller 102.

Control starts at block 501 in which the cache management application132 sets a read hit counter for the bottom portion of the syncio LRUlist 212 and a read hit counter for the bottom portion of the non-syncioLRU list 206 to zero. Control proceeds to block 502 in which a readoperation generates a read hit on the cache 112, and control proceeds inparallel to block 504 and 506. At block 504, the cache managementapplication 132 determines whether the read hit is on the bottom portionof the syncio LRU list 212 and if so (“Yes” branch 508) a read hitcounter for the bottom portion of the syncio list 212 is incremented (atblock 510). Otherwise (“No” branch 512), control returns to block 502.

At block 506, the cache management application 132 determines whetherthe read hit is on the bottom portion of the non-syncio LRU list 206 andif so (“Yes” branch 514) a read hit counter for the bottom portion ofthe non-syncio list 206 is incremented (at block 516). Otherwise (“No”branch 518), control returns to block 502. The operations of block 501,502, 504, 506, 508, 510, 512, 514, 516. 518 are performed for aninterval of time (e.g., 800 milliseconds) repeatedly (as shown viareference numeral 520).

While the operations shown via reference numeral 520 are beingperformed, the operations shown in blocks 522 and 524 are performed. Atblock 522 the cache management application 132 computes the read hitratio for the bottom portion of syncio list 212 by adding the read hitsfor the last N number of intervals and dividing by the cumulative timefor those intervals. At block 524 the cache management application 132computes the read hit ratio for the bottom portion of the non-synciolist 206 by adding the read hits for the last N number of intervals anddividing by the cumulative time for those intervals. In certainembodiments N may be a number such as 30.

Therefore, FIG. 5 illustrates certain embodiments for computing the readhit ratio on bottom portions of the non-syncio LRU list 134 and syncioLRU list 136 for using in the operations shown in FIG. 4.

FIG. 6 illustrates a block diagram 600 that shows how a predeterminedfactor for demotion of tracks is computed, in accordance with certainembodiments. Exemplary predetermined factors have been shown to be usedin block 312 of FIG. 3, and block 428 of FIG. 4.

In certain embodiments, the predetermined factor may be based onperformance benchmarks of the system (as shown via reference numeral602). In other embodiments, the predetermined factor may be configuredby customers who desire better performance for syncio workloads overnon-syncio workloads (as shown via reference numeral 604). In yetfurther embodiments, the predetermined factor may be dynamically changedbased on the rate of I/O operations occurring the storage controller 102(as shown via reference numeral 606). For example, if the rate of I/Ooperations increase as the predetermined factor is increased than thecache management application 132 keeps increasing the predeterminedfactor, and if the rate of I/O operations decrease as the predeterminedfactor is increased then the cache management application 132 keepsdecreasing the predetermined factor.

FIG. 7 illustrates a flowchart 700 that shows demotion of tracks basedon generating lists of two different types of tracks, in accordance withcertain embodiments. The operations shown in FIG. 7 may be performed bythe cache management application 132 that executes in the storagecontroller 102.

Control starts at block 702 in which a list of a first type of tracks(e.g. syncio LRU list 136) in a cache 112 is generated. Control proceedsto block 704 in which a list of a second type of tracks (non-syncio LRUlist 134) in the cache 112 is generated, wherein I/O operations arecompleted relatively faster to the first type of tracks than to thesecond type of tracks, and wherein a track is added to the list of thefirst type of tracks or to the list of the second type of tracks basedon whether a last I/O operation performed on the track is a first typeof I/O operation (e.g., syncio operation) or a second type of I/Ooperation (e.g. non-syncio operation). For example, if the last I/Ooperation performed on a track is a syncio operation then the track isadded to the syncio LRU list 136, and if the last I/O operationperformed on a track is a non-syncio operation then the track is addedto the non-syncio LRU list 134. A determination is made (at block 706)as to whether to demote a track from the list of the first type oftracks or from the list of the second type of tracks. The first type oftracks may be syncio tracks, where for performing an I/O operation to asyncio track, an application thread is held in a spin loop waiting forthe I/O operation to complete. The second type of tracks may benon-syncio tracks, where for performing the I/O operation to anon-syncio track, holding of the application thread in the spin loop isavoided.

In certain embodiments, tracks in the list of the first type of tracksare ordered based on how recently each track in the list of the firsttype of tracks has been used (e.g., as shown via reference numerals 208,210), wherein tracks in the list of the second type of tracks areordered based on how recently each track in the list of the second typeof tracks has been used (e.g., as shown via reference numerals 202,204), where a track is said to be used if a read hit has occurred on thetrack.

To perform the determination on track demotion shown in block 706, incertain embodiments, in response to determining that a read hit ratiofor tracks in the list of the second type of tracks is less than apredetermined factor of a read hit ratio for tracks in the first type oftracks, a track is demoted (at block 708) from the list of the secondtype of tracks. The read hit ratio for tracks in the list of the firsttype of tracks and the read hit ratio for tracks in the list of thesecond type of tracks are computed based on read hits on a predeterminedbottom portion of the list of the first type of tracks and the secondtype of tracks. The predetermined factor is adjusted to increase a rateof input/output (I/O) operations.

Therefore, FIGS. 1-7 illustrate certain embodiments in which bymaintaining separate LRU lists for syncio tracks and non-syncio tracksand using demotion mechanisms based on the separate LRU lists, synciooperations are completed faster in comparison to embodiments in whichonly a single LRU list is maintained. In certain embodiments, wheneverit is possible, tracks from the LRU list of non-syncio tracks(non-syncio LRU list 134) are demoted rather than tracks from the LRUlist of syncio tracks (syncio LRU list 136), unless the rate of I/Ooperations in the system decrease as a result of such demotions.

Cloud Computing Environment

Cloud computing is a model for enabling convenient, on-demand networkaccess to a shared pool of configurable computing resources (e.g.,networks, servers, storage, applications, and services) that can berapidly provisioned and released with minimal management effort orservice provider interaction.

Referring now to FIG. 8 an illustrative cloud computing environment 50is depicted. As shown, cloud computing environment 50 comprises one ormore cloud computing nodes 10 with which local computing devices used bycloud consumers, such as, for example, personal digital assistant (PDA)or cellular telephone 54A, desktop computer 54B, laptop computer 54C,and/or automobile computer system 54N may communicate. Nodes 10 maycommunicate with one another. They may be grouped (not shown) physicallyor virtually, in one or more networks, such as Private, Community,Public, or Hybrid clouds as described hereinabove, or a combinationthereof. This allows cloud computing environment 50 to offerinfrastructure, platforms and/or software as services for which a cloudconsumer does not need to maintain resources on a local computingdevice. It is understood that the types of computing devices 54A-N shownin FIG. 8 are intended to be illustrative only and that computing nodes10 and cloud computing environment 50 can communicate with any type ofcomputerized device over any type of network and/or network addressableconnection (e.g., using a web browser).

Referring now to FIG. 9, a set of functional abstraction layers providedby cloud computing environment 50 (FIG. 8) is shown. It should beunderstood in advance that the components, layers, and functions shownin FIG. 9 are intended to be illustrative only and embodiments of theinvention are not limited thereto.

Hardware and software layer 60 includes hardware and softwarecomponents. Examples of hardware components include mainframes, in oneexample IBM zSeries* systems; RISC (Reduced Instruction Set Computer)architecture based servers, in one example IBM pSeries* systems; IBMxSeries* systems; IBM BladeCenter* systems; storage devices; networksand networking components. Examples of software components includenetwork application server software, in one example IBM WebSphere*application server software; and database software, in one example IBMDB2* database software.

Virtualization layer 62 provides an abstraction layer from which thefollowing examples of virtual entities may be provided: virtual servers;virtual storage; virtual networks, including virtual private networks;virtual applications and operating systems; and virtual clients.

In one example, management layer 64 may provide the functions describedbelow. Resource provisioning provides dynamic procurement of computingresources and other resources that are utilized to perform tasks withinthe cloud computing environment. Metering and Pricing provide costtracking as resources are utilized within the cloud computingenvironment, and billing or invoicing for consumption of theseresources. In one example, these resources may comprise applicationsoftware licenses. Security provides identity verification for cloudconsumers and tasks, as well as protection for data and other resources.User portal provides access to the cloud computing environment forconsumers and system administrators. Service level management providescloud computing resource allocation and management such that requiredservice levels are met. Service Level Agreement (SLA) planning andfulfillment provide pre-arrangement for, and procurement of, cloudcomputing resources for which a future requirement is anticipated inaccordance with an SLA.

Workloads layer 66 provides examples of functionality for which thecloud computing environment may be utilized. Examples of workloads andfunctions which may be provided from this layer include: mapping andnavigation; software development and lifecycle management; virtualclassroom education delivery; data analytics processing; transactionprocessing; and processing of demote operations 68 as shown in FIGS.1-8.

Additional Embodiment Details

The described operations may be implemented as a method, apparatus orcomputer program product using standard programming and/or engineeringtechniques to produce software, firmware, hardware, or any combinationthereof. Accordingly, aspects of the embodiments may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” Furthermore,aspects of the embodiments may take the form of a computer programproduct. The computer program product may include a computer readablestorage medium (or media) having computer readable program instructionsthereon for causing a processor to carry out aspects of the presentembodiments.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present embodiments may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present embodiments.

Aspects of the present embodiments are described herein with referenceto flowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instruction.

FIG. 10 illustrates a block diagram that shows certain elements that maybe included in the storage controller 102 or the hosts 104, 106, orother computational devices in accordance with certain embodiments. Thesystem 1000 may include a circuitry 1002 that may in certain embodimentsinclude at least a processor 1004. The system 1000 may also include amemory 1006 (e.g., a volatile memory device), and storage 1008. Thestorage 1008 may include a non-volatile memory device (e.g., EEPROM,ROM, PROM, flash, firmware, programmable logic, etc.), magnetic diskdrive, optical disk drive, tape drive, etc. The storage 1008 maycomprise an internal storage device, an attached storage device and/or anetwork accessible storage device. The system 1000 may include a programlogic 1010 including code 1012 that may be loaded into the memory 1006and executed by the processor 1004 or circuitry 1002. In certainembodiments, the program logic 1010 including code 1012 may be stored inthe storage 1008. In certain other embodiments, the program logic 1010may be implemented in the circuitry 1002. One or more of the componentsin the system 1000 may communicate via a bus or via other coupling orconnection 1014. Therefore, while FIG. 10 shows the program logic 1010separately from the other elements, the program logic 1010 may beimplemented in the memory 1006 and/or the circuitry 1002.

Certain embodiments may be directed to a method for deploying computinginstruction by a person or automated processing integratingcomputer-readable code into a computing system, wherein the code incombination with the computing system is enabled to perform theoperations of the described embodiments.

The terms “an embodiment”, “embodiment”, “embodiments”, “theembodiment”, “the embodiments”, “one or more embodiments”, “someembodiments”, and “one embodiment” mean “one or more (but not all)embodiments of the present invention(s)” unless expressly specifiedotherwise.

The terms “including”, “comprising”, “having” and variations thereofmean “including but not limited to”, unless expressly specifiedotherwise.

The enumerated listing of items does not imply that any or all of theitems are mutually exclusive, unless expressly specified otherwise.

The terms “a”, “an” and “the” mean “one or more”, unless expresslyspecified otherwise.

Devices that are in communication with each other need not be incontinuous communication with each other, unless expressly specifiedotherwise. In addition, devices that are in communication with eachother may communicate directly or indirectly through one or moreintermediaries.

A description of an embodiment with several components in communicationwith each other does not imply that all such components are required. Onthe contrary a variety of optional components are described toillustrate the wide variety of possible embodiments of the presentinvention.

Further, although process steps, method steps, algorithms or the likemay be described in a sequential order, such processes, methods andalgorithms may be configured to work in alternate orders. In otherwords, any sequence or order of steps that may be described does notnecessarily indicate a requirement that the steps be performed in thatorder. The steps of processes described herein may be performed in anyorder practical. Further, some steps may be performed simultaneously.

When a single device or article is described herein, it will be readilyapparent that more than one device/article (whether or not theycooperate) may be used in place of a single device/article. Similarly,where more than one device or article is described herein (whether ornot they cooperate), it will be readily apparent that a singledevice/article may be used in place of the more than one device orarticle or a different number of devices/articles may be used instead ofthe shown number of devices or programs. The functionality and/or thefeatures of a device may be alternatively embodied by one or more otherdevices which are not explicitly described as having suchfunctionality/features. Thus, other embodiments of the present inventionneed not include the device itself.

At least certain operations that may have been illustrated in thefigures show certain events occurring in a certain order. In alternativeembodiments, certain operations may be performed in a different order,modified or removed. Moreover, steps may be added to the above describedlogic and still conform to the described embodiments. Further,operations described herein may occur sequentially or certain operationsmay be processed in parallel. Yet further, operations may be performedby a single processing unit or by distributed processing units.

The foregoing description of various embodiments of the invention hasbeen presented for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed. Many modifications and variations are possible in lightof the above teaching. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto. The above specification, examples and data provide acomplete description of the manufacture and use of the composition ofthe invention. Since many embodiments of the invention can be madewithout departing from the spirit and scope of the invention, theinvention resides in the claims hereinafter appended.

* IBM, zSeries, pSeries, xSeries, BladeCenter, WebSphere, and DB2 aretrademarks of International Business Machines Corporation registered inmany jurisdictions worldwide.

What is claimed is:
 1. A method, comprising: generating a list of afirst type of tracks in a cache; generating a list of a second type oftracks in the cache, wherein a track is added to the list of the firsttype of tracks or to the list of the second type of tracks based onwhether a last I/O operation performed on the track is a first type ofI/O operation or a second type of I/O operation; and determining whetherto demote a track from the list of the first type of tracks or from thelist of the second type of tracks, wherein: for performing the firsttype of I/O operation to a first type of track, an application thread isheld in a spin loop waiting for the first type of I/O operation tocomplete; and for performing the second type of I/O operation to asecond type of track, holding of the application thread in the spin loopis avoided.
 2. The method of claim 1, wherein the first type of tracksare syncio tracks.
 3. The method of claim 2, wherein the second type oftracks are non-syncio tracks.
 4. The method of claim 3, wherein tracksin the list of the first type of tracks are ordered based on howrecently each track in the list of the first type of tracks has beenused, and wherein tracks in the list of the second type of tracks areordered based on how recently each track in the list of the second typeof tracks has been used.
 5. The method of claim 4, the method furthercomprising: in response to determining that a read hit ratio for tracksin the list of the second type of tracks is less than a predeterminedfactor of a read hit ratio for tracks in the first type of tracks,demoting a track from the list of the second type of tracks.
 6. Themethod of claim 5, wherein the read hit ratio for tracks in the list ofthe first type of tracks and the read hit ratio for tracks in the listof the second type of tracks are computed based on read hits on apredetermined bottom portion of the list of the first type of tracks andthe second type of tracks.
 7. The method of claim 5, the method furthercomprising: adjusting the predetermined factor to increase a rate ofinput/output (I/O) operations.
 8. A system, comprising: a memory; and aprocessor coupled to the memory, wherein the processor performsoperations, the operations performed by the processor comprising:generating a list of a first type of tracks in a cache; generating alist of a second type of tracks in the cache, wherein a track is addedto the list of the first type of tracks or to the list of the secondtype of tracks based on whether a last I/O operation performed on thetrack is a first type of I/O operation or a second type of I/Ooperation; and determining whether to demote a track from the list ofthe first type of tracks or from the list of the second type of tracks,wherein: for performing the first type of I/O operation to a first typeof track, an application thread is held in a spin loop waiting for thefirst type of I/O operation to complete; and for performing the secondtype of I/O operation to a second type of track, holding of theapplication thread in the spin loop is avoided.
 9. The system of claim8, wherein the first type of tracks are syncio tracks.
 10. The system ofclaim 9, wherein the second type of tracks are non-syncio tracks,wherein for performing the I/O operation to a non-syncio track.
 11. Thesystem of claim 10, wherein tracks in the list of the first type oftracks are ordered based on how recently each track in the list of thefirst type of tracks has been used, and wherein tracks in the list ofthe second type of tracks are ordered based on how recently each trackin the list of the second type of tracks has been used.
 12. The systemof claim 11, the operations further comprising: in response todetermining that a read hit ratio for tracks in the list of the secondtype of tracks is less than a predetermined factor of a read hit ratiofor tracks in the first type of tracks, demoting a track from the listof the second type of tracks.
 13. The system of claim 12, wherein theread hit ratio for tracks in the list of the first type of tracks andthe read hit ratio for tracks in the list of the second type of tracksare computed based on read hits on a predetermined bottom portion of thelist of the first type of tracks and the second type of tracks.
 14. Thesystem of claim 12, the operations further comprising: adjusting thepredetermined factor to increase a rate of input/output (I/O)operations.
 15. A computer program product, the computer program productcomprising a computer readable storage medium having computer readableprogram code embodied therewith, the computer readable program codeconfigured to perform operations, the operations comprising: generatinga list of a first type of tracks in a cache; generating a list of asecond type of tracks in the cache, wherein a track is added to the listof the first type of tracks or to the list of the second type of tracksbased on whether a last I/O operation performed on the track is a firsttype of I/O operation or a second type of I/O operation; and determiningwhether to demote a track from the list of the first type of tracks orfrom the list of the second type of tracks, wherein: for performing thefirst type of I/O operation to a first type of track, an applicationthread is held in a spin loop waiting for the first type of I/Ooperation to complete; and for performing the second type of I/Ooperation to a second type of track, holding of the application threadin the spin loop is avoided.
 16. The computer program product of claim15, wherein the first type of tracks are syncio tracks.
 17. The computerprogram product of claim 16, wherein the second type of tracks arenon-syncio tracks.
 18. The computer program product of claim 17, whereintracks in the list of the first type of tracks are ordered based on howrecently each track in the list of the first type of tracks has beenused, and wherein tracks in the list of the second type of tracks areordered based on how recently each track in the list of the second typeof tracks has been used.
 19. The computer program product of claim 18,the operations further comprising: in response to determining that aread hit ratio for tracks in the list of the second type of tracks isless than a predetermined factor of a read hit ratio for tracks in thefirst type of tracks, demoting a track from the list of the second typeof tracks.
 20. The computer program product of claim 19, wherein theread hit ratio for tracks in the list of the first type of tracks andthe read hit ratio for tracks in the list of the second type of tracksare computed based on read hits on a predetermined bottom portion of thelist of the first type of tracks and the second type of tracks.
 21. Thecomputer program product of claim 19, the operations further comprising:adjusting the predetermined factor to increase a rate of input/output(I/O) operations.
 22. A storage controller, comprising: a cache; and acache management application maintained in the storage controller,wherein the cache management application performs operations, theoperations comprising: generating a list of a first type of tracks inthe cache; generating a list of a second type of tracks in the cache,wherein a track is added to the list of the first type of tracks or tothe list of the second type of tracks based on whether a last I/Ooperation performed on the track is a first type of I/O operation or asecond type of I/O operation; and determining whether to demote a trackfrom the list of the first type of tracks or from the list of the secondtype of tracks, wherein: for performing the first type of I/O operationto a first type of track, an application thread is held in a spin loopwaiting for the first type of I/O operation to complete; and forperforming the second type of I/O operation to a second type of track,holding of the application thread in the spin loop is avoided.
 23. Thestorage controller of claim 22, wherein the first type of tracks aresyncio tracks.
 24. The storage controller of claim 23, wherein thesecond type of tracks are non-syncio tracks.
 25. The storage controllerof claim 24, wherein tracks in the list of the first type of tracks areordered based on how recently each track in the list of the first typeof tracks has been used, and wherein tracks in the list of the secondtype of tracks are ordered based on how recently each track in the listof the second type of tracks has been used.